Question

Explain the vascular tissue system.

Answer 1

Hint: The vascular tissue system refers to the xylem and phloem of plants. These are conducting tissues having a vessel-like appearance that form vascular bundles. The vascular tissue system is responsible for water and nutrition transport in plants. Vascular tissue occurs in three distinct patches.

Complete answer: Xylem and phloem make up the vascular tissue system in plants. Xylem is water-conducting vascular tissues and phloem is a food conducting and storing the type of vascular tissue. Both of these tissues act in coordination to perform various transportation functions in plants. The elements of xylem and phloem are organized in a group and constitute the vascular bundle. Xylem and phloem with cambium are called open vascular bundles and without cambium are called closed vascular bundles. These vascular bundles or tissue are divided into three main types called radial, conjoint, and concentric.

Let us now understand each of the vascular bundle types in detail.
The strands of vascular tissue known as vascular strands or cylinders occur in distinct patches in gymnosperms called vascular bundles.
Radial bundles- In this type of vascular bundle, the xylem and phloem individually form the xylem bundles and phloem bundles. These two types of bundles are arranged alternatively to each other. Both of these occur in different radii. These bundles are characteristics of the roots of plants.
Conjoint bundles- As the name suggests in this type of vascular bundle the xylem and phloem both are present in a conjoined manner. These are further of three types:
i. Collateral bundles- The phloem and xylem lie on the same radii with the xylem on the inner side and the phloem on the outer side. A strip of vascular cambium occurs in the xylem and phloem in dicot stems. This is called intrafascicular cambium. The cambium develops to form secondary tissues. This makes open vascular bundles. In monocots, cambium is absent and thus the vascular bundles are termed closed.
ii. Bicollateral bundles- In this type of vascular bundle the phloem lies on the outer as well as the inner side of the xylem on the same radii. A strip of cambium may be present both on the outer and inner side of the xylem. This type of vascular bundle is seen in pumpkin.
iii. Concentric bundles- This is a unique type of vascular bundle in which either xylem or phloem forms a solid core and one of them surrounds the other completely. A vascular cambium strip is always present in this vascular bundle. These are of two types:
a. Amphicribal bundle- It is also called a hadrocentric bundle. The xylem forms the central core. Phloem acts as surrounding tissue.
b. Amphivasal bundle- It is also known as the leptocentric bundle. In this, the xylem surrounds the phloem that lies in the center.

Note: The vascular bundles are the most important parts of a plant. These not only provide a transportation way for water and nutrients but also provide mechanical support to plants. The amphicribral bundle is seen in aquatic angiosperms and Prunus which is a dicot. Amphivasal bundle is seen in Yucca, Dracaena, etc.